I agree with GP that foreign buyers are mostly a scapegoat, but unlike GP, I do believe zoning is the main issue. Giving zoning power to local politics will always end up with the same issue. Rich homeowners voting for board members who pass laws which limit supply, resulting in the value of their assets going up. It's the same issue all over the world. Single detached houses do not belong in cities.

This is a great playlist around the subject:

https://www.youtube.com/playlist?list=PLTNrJFli7ocgtZNW5IzFs...